Controlled layer-by-layer formation of ultrathin oxide films on silver island films for surface-enhanced Raman scattering measurement

Methods for the controlled deposition of ultrathin metal oxide layers onto silver island films for surface-enhanced Raman scattering (SERS) measurements are reported. Two related deposition techniques are explored for thin film growth: a surface sol-gel method and atomic layer deposition. Both methods exhibit excellent control of the deposited film thickness to atomic level precision while conformally coating the complex structures found in silver island films. Coating of metal oxide films onto silver substrates provides a method for monitoring the distance dependence of SERS enhancements and offers a platform for exploring adsorption and interaction of analytes on dielectric surfaces. Analysis of the distance dependence of the Raman signal with increasing film thickness yields estimated silver particle sizes that are in agreement with microscopy, which is consistent with the layer-by-layer growth mechanism of uniform metal oxide films on the silver substrate. These methods can be easily extended to grow a variety of laminar or mixed metal oxide films for the exploration of interfacial phenomena.